U.S. patent number 5,719,567 [Application Number 08/453,720] was granted by the patent office on 1998-02-17 for system for enhancing navigation and surveillance in low visibility conditions.
This patent grant is currently assigned to Victor J. Norris, Jr.. Invention is credited to Victor J. Norris.
United States Patent |
5,719,567 |
Norris |
February 17, 1998 |
System for enhancing navigation and surveillance in low visibility
conditions
Abstract
A system for enhancing navigation or surveillance in low
visibility conditions is realized by employing one or more
ultraviolet radiation sources, a receiver which is capable of
producing output signals from which a two dimensional image of the
received radiation can be constructed, and a display device for
displaying such image. In one preferred embodiment the ultraviolet
radiation source is co-positioned with a critical marker such as a
runway beacon or hazard beacon. The ultraviolet radiation emanates
from the source, preferably modulated to form a repetitive,
characteristic signal, propagates through the low visibility
atmosphere, and received by the ultraviolet imaging receiver. In
another preferred embodiment, an ultraviolet radiation source is
placed at or near the ultraviolet imaging receiver, that is,
onboard the same vehicle or at the same fixed location. One or more
reflectors are co-positioned with the critical markers. The
reflector reflects or redirect an ultraviolet radiation signal,
received from the source, back through the low visibility
atmosphere to the ultraviolet imaging receiver whereby an image of
the received radiation is presented to an operator by a display
device. In another preferred embodiment, the reflector may be
replaced with a transponder. The present invention permits a pilot,
vehicle operator, air traffic controller, or other operator to
perform navigation or surveillance tasks in low visibility
conditions in similar manner to that employed under clear weather
conditions.
Inventors: |
Norris; Victor J. (Ellicott
City, MD) |
Assignee: |
Norris, Jr.; Victor J.
(Ellicott City, MD)
|
Family
ID: |
23801781 |
Appl.
No.: |
08/453,720 |
Filed: |
May 30, 1995 |
Current U.S.
Class: |
340/953; 250/372;
342/33; 340/952; 340/956; 398/115; 398/106 |
Current CPC
Class: |
G01S
7/48 (20130101); G01S 1/7032 (20190801); G08G
5/025 (20130101); G01S 17/74 (20130101); G08G
5/0021 (20130101); G01S 17/933 (20130101); G01S
17/95 (20130101); G01S 1/70 (20130101); G01S
17/89 (20130101); Y02A 90/10 (20180101); G01S
17/88 (20130101) |
Current International
Class: |
G01S
17/74 (20060101); G01S 17/00 (20060101); G08G
5/00 (20060101); G01S 7/48 (20060101); G01S
17/95 (20060101); G01S 17/88 (20060101); G01S
17/89 (20060101); G01S 17/93 (20060101); B64F
001/18 () |
Field of
Search: |
;340/947,948,952,953,956
;73/178T ;342/33 ;250/372,54R ;359/154,169 ;356/152.3 |
References Cited
[Referenced By]
U.S. Patent Documents
Other References
Michael Muehlemann, "Tungsten Halogen for Illumination", The
Photonics Design and Applications Handbook, 1993, pp. H-329 to
H-330. .
Cooper Industries Product Brochure, "HRLQ High Intensity Runway
Light/Quartz", Mar. 1991. .
Godfrey Engineering Product Brochure, "Reils Three Intensity Model
GE3836-0003", Undated. .
Applications, Accessories & Support Brochure, "UV-Sensitive
Solar Blind Photo Multiplier Tubes", EMR Photoelectric, Undated.
.
Schlumberger Product Brochure, "Custom Designed Microchannel [Late
Tubes]", Undated..
|
Primary Examiner: Swarthout; Brent A.
Attorney, Agent or Firm: De La Rosa; J.
Claims
I claim:
1. A system for locating in a low visibility atmosphere an object
having at least one identifying marker, said system comprising:
means co-located with said at least one identifying marker for
emitting ultraviolet radiation substantially in the solar blind
region that penetrates the low visibility atmosphere, wherein water
present in fog causing said low visibility atmosphere interacts
with and breaks down the ozone therein so as to reduce the
attenuation attributable to the ozone in said atmosphere of the
emitted ultraviolet radiation, said means for emitting positioned
so as to establish the location of the object within a desired
field of view;
means responsive to said ultraviolet radiation for creating an
image of said means for emitting, said image depicting the location
of said object within the desired field of view; and
means for processing said image so as to remove associated
radiation from objects also emitting within the solar blind
region.
2. The system of claim 1 further comprising means for displaying a
representation of said image.
3. The system of claim 2 wherein said means for displaying includes
a head-up display wherein said representation is superimposed over
a visual image of said at least one critical marker.
4. The system of claim 1 wherein said means for creating an image
includes a microchannel plate photomultiplier tube.
5. The system of claim 1 further comprising means for focusing said
ultraviolet radiation onto said means for creating an image.
6. The system of claim 5 wherein said means for focusing includes a
lens.
7. The system of claim 1 wherein said means for processing includes
a signal processor.
8. The system of claim 1 further comprising means for modulating
said ultraviolet radiation in accordance with a characteristic of
said at least one identifying marker.
9. The system of claim 1 wherein said means for creating an image
comprises means for selectively blocking out radiation
approximately above 0.275 .mu.m.
10. The system of claim 9 wherein said means for selectively
filtering includes an absorption filter.
11. The system of claim 1 wherein said means for emitting comprises
means for directing the ultraviolet radiation along a predetermined
solid angle of illumination and at a desired elevation.
12. The system of claim 1 wherein said at least one identifying
marker includes an airport structure.
13. The system of claim 12 wherein said airport structure includes
runway beacons and lights.
14. The system of claim 1 wherein said means for creating an image
is located on an aircraft.
15. The system of claim 1 wherein said means for creating an image
is located in a control tower.
16. The system of claim 1 wherein said means for emitting is
located on an aircraft.
17. The system of claim 1 wherein said means for emitting is
integrated with the structure of said least one identifying
marker.
18. The system of claim 1 wherein said means for emitting is
selected from a group consisting of xenon, quartz mercury, tungsten
halogen or deuterium lamps.
19. The system of claim 1 wherein said means for emitting includes
a laser.
20. The system of claim 19 wherein said laser is an ultraviolet
laser.
21. A system for enhancing navigation in a low visibility
atmosphere, wherein water present in fog causing the low visibility
atmosphere interacts with and breaks down the ozone therein so as
to reduce the attenuation attributable to the ozone in said
atmosphere of emitted ultraviolet radiation, said system
comprising:
a plurality of sources co-located with critical markers of a
desired area so as to establish the location of the desired area
within a desired field of view, said plurality of sources emitting
ultraviolet radiation substantially in the solar blind region;
means responsive to said ultraviolet radiation for imaging said
plurality of sources so as to form an image thereof showing the
location of the desired area within the desired field of view;
and
means for displaying said image to an observer, said image
providing a navigation reference.
22. The system of claim 21 further comprising means for processing
said image.
23. The system of claim 21 wherein said means for imaging includes
a microchannel plate photomultiplier tube.
24. The system of claim 21 further comprising means for modulating
said ultraviolet radiation from said plurality of sources.
25. The system of claim 21 wherein said means for imaging includes
means for blocking out radiation approximately above 0.275
.mu.m.
26. A system for navigating in a low visibility atmosphere, wherein
water present in fog causing the low visibility atmosphere
interacts with and breaks down the ozone therein so as to reduce
the attenuation attributable to the ozone in said atmosphere of
emitted ultraviolet radiation, said system comprising:
a plurality of reflectors co-positioned with critical markers of a
desired area, said critical marker fixing the location of the
desired area within a desired field of view;
a source emitting radiation substantially along a direction to said
plurality of reflectors, said radiation substantially within the
solar blind region of the ultraviolet radiation spectrum;
means responsive to radiation reflected from said plurality of
reflectors for forming an image of said plurality of reflectors
depicting the location of said desired area within the desired
field of view, said means for forming an image co-located with said
source; and
means for displaying a representation of said image, whereby said
representation provides a navigation reference to an observer.
27. The system of claim 26 wherein said means for forming an image
comprises an optical filter having a bandpass region substantially
between 0.205 .mu.m-0.275 .mu.m.
28. The system of claim 26 wherein said plurality of reflectors
includes retroreflectors.
29. The system of claim 26 further comprising means for processing
said image.
30. The system of claim 26 wherein said means for forming an image
includes a microchannel plate photomultiplier tube.
31. The system of claim 26 further comprising means for modulating
said ultraviolet radiation from said source.
32. The system of claim 26 further comprising means for modulating
said ultraviolet radiation reflected from said plurality of
reflectors.
33. The system of claim 26 wherein said means for forming an image
includes means for electronically filtering out signals
corresponding to radiation substantially between 0.205-0.270 .mu.m
and having a desired modulation.
34. The system of claim 26 further comprising means for gating such
that backscattering for the radiation from said source is
substantially reduced.
35. A system for use in a low visibility atmosphere, wherein water
present in fog causing the low visibility atmosphere interacts with
and breaks down the ozone therein so as to reduce the attenuation
attributable to the ozone in said atmosphere of emitted ultraviolet
radiation, said system comprising:
a plurality of transponders co-positioned with critical markers of
a desired area, said critical markers positioned so as to establish
the location of the desired area within a desired field of
view;
a source emitting a first radiation substantially along a direction
to said plurality of transponders, said transponders in response to
said first radiation emitting a second radiation, said first and
second radiation within the solar blind region of the ultraviolet
radiation spectrum; and
means responsive to said second radiation for forming an image of
said plurality of transponders depicting the location of the
desired area within the desired field of view, said means for
forming an image co-located with said source.
36. The system of claim 35 wherein said first and second radiation
have different wavelengths.
37. The system of claim 35 further comprising means for displaying
a representation of said image, whereby said representation
provides a navigation reference to an observer.
38. The system of claim 35 wherein said means for displaying
includes a head-up display.
39. The system of claim 35 wherein said means for forming an image
includes a microchannel plate photomultiplier tube.
40. The system of claim 35 further comprising means for processing
said image for removing radiation associated with objects emitting
in the solar blind region.
41. The system of claim 35 further comprising means for modulating
said second radiation in accordance with characteristics of said
critical markers.
42. The system of claim 35 wherein said means for forming an image
comprises means for selectively blocking out radiation
approximately above 0.275 .mu.m.
43. The system of claim 35 wherein said critical markers include an
airport structure.
44. The system of claim 43 wherein said airport structure includes
runway beacons and lights.
45. The system of claim 35 wherein said means for forming an image
is located on an aircraft.
46. The system of claim 35 wherein said means for forming an image
is located in a control tower.
47. A method for locating in a low visibility atmosphere an object
having at least one identifying marker, said method comprising the
steps of:
co-positioning with said at least one identifying marker of a
desired area a source for emitting ultraviolet radiation
substantially in the solar blind region that penetrates the low
visibility atmosphere, wherein water present in fog causing said
low visibility atmosphere interacts with and breaks down the ozone
therein so as to reduce the attenuation attributable to the ozone
in said atmosphere of the emitted ultraviolet radiation, said at
least one identifying marker establishing the location of the
desired area within a desired field of view;
forming an image of said source from radiation received therefrom,
said image showing the location of the desired area within the
desired field of view; and
displaying a representation of said image.
48. The method of claim 47 further comprising the step of
superimposing said representation of said image over an actual
visual image of said at least one critical marker.
49. The method of claim 47 further comprising the step of
processing said image.
50. The method of claim 47 further comprising the step of
modulating said ultraviolet radiation in accordance with a
characteristic of said at least one identifying marker.
51. The method of claim 47 wherein said step of forming an image
includes the step of blocking out radiation approximately above
0.275 .mu.m.
52. The method of claim 47 wherein the source for emitting
ultraviolet radiation is a laser.
53. A method for navigating in a low visibility atmosphere, wherein
water present in fog causing said low visibility atmosphere
interacts with and breaks down the ozone therein so as to reduce
the attenuation attributable to the ozone in the atmosphere of
emitted ultraviolet radiation, said method comprising the steps
of:
co-positioning a plurality of reflectors with critical markers of a
desired area, said critical markers establishing the location of
the desired area within a desired field of view;
emitting radiation from a source substantially along a direction to
said plurality of reflectors, said radiation substantially within
the solar blind region of the ultraviolet radiation spectrum;
forming from radiation reflected from said plurality of reflectors
an image thereof depicting the location of the desired area within
the desired field of view; and
displaying a representation of said image, whereby said
representation provides a navigation reference to an observer.
54. The method of claim 53 wherein said step of forming an image
includes the step of blocking out radiation approximately above
0.275 .mu.m.
55. The method of claim 53 further comprising the step of
processing said image.
56. The method of claim 53 further comprising the step of
modulating the ultraviolet radiation from said source.
57. The method of claim 53 further comprising the step of
modulating the ultraviolet radiation reflected from said plurality
of reflectors.
Description
TECHNICAL FIELD
This invention relates to a system for enhancing navigation or
surveillance, and more particularly, to a system for providing the
location and characteristics of relevant objects and/or areas, such
as aircraft and runway lights, useful under low visibility
conditions.
BACKGROUND OF THE INVENTION
Under clear weather conditions, light propagates through the
atmosphere with only a slight loss due to absorption and
scattering. However, when aerosols and molecules that contribute to
various adverse weather conditions, such as fog, rain, or snow, are
present in the atmosphere in sufficient number, they may absorb and
scatter light to the extent that the losses are significant and the
visibility is seriously degraded. In various situations, such
visibility can present costly disruptions and a dangerous lack of
information concerning the location and characteristics of critical
objects and/or areas.
In the prior art, systems have been used to supplement the human
eye in locating and perceiving objects and/or areas under adverse
weather conditions. Ideally, such systems possess the ability to
"penetrate" the weather, that is, provide information on the
location and characteristics of the desired objects and/or areas to
an operator in the same context as that obtainable in clear
weather.
Such systems are of particular importance to aviation where poor
visibility conditions develop spontaneously and demand time
critical reaction. Despite sophisticated and costly avionics,
weather conditions still impose limitations on final approaches to
landing. These limitations account for the capabilities of the
aircraft, the pilot and the equipment installed at the airport.
Each set of capabilities is associated with a minimum ceiling and a
minimum runway visibility before landing is permitted. Operating
under instrument flight rules (IFR), a pilot can be guided to a
specified distance from the runway by indications of glide-path
deviations presented on the aircraft's instrument panel. Such
glide-path deviations are typically provided by landing guidance
systems, such as instrument landing systems (ILS), microwave
landing systems (MLS) or global positioning systems (GPS/GNSS) that
are linked to the aircraft via radio frequency (RF) transmissions.
If at a specified distance, the pilot is unable to see the
characteristics of the runway as set by the FAA, the pilot must
execute a missed approach. To minimize these incidents, air traffic
controllers frequently re-route the aircraft or do not provide
takeoff clearance to an aircraft destined for an affected airport.
Whatever the alternative, these procedures prompt anxiety in the
passengers and flight crews, impose additional expense, result in
delays and scheduling disruptions, and reduce operational safety
margins.
As visibility degrades and landing conditions transform from
Category I, through Category II, to various grades of Category III,
the pilot's capability to operate the aircraft is augmented by
increasing levels of equipment sophistication. This accommodation
is in recognition of a more demanding criteria for the required
navigation performance (RNP) as runway visual range decreases. One
level of equipment sophistication involves an autopilot that aids
in the operation of the flight controls. Ideally, in Category III
conditions, the glide path deviations can be directly coupled to
the aircraft through the autopilot such that the aircraft descends
to the runway and flares automatically with the pilot "out of the
loop." In actual practice, however, this "out of the loop" mode is
seldom invoked due to the high cost of implementation. The RNP in
this instance imposes stringent certification criteria in terms of
integrity, availability, continuity of service, and accuracy.
Equipment cost and maintenance, as well as continued proficiency
training necessary for compliance, limit its cost
effectiveness.
A variety of systems have attempted to solve the inherent
disadvantages of RF linked, guidance error based systems. One of
the simplest approaches is the use of pulsed, intense white beacons
for runway approach and threshold indications. While beneficial for
long range detection, this approach has proved to be detrimental at
close ranges, especially in dense fog. On a short final approach,
the intense white beacons generally blind the pilot and fail to
provide any spatial orientation due to atmospheric diffusion at
visible wavelengths.
Active optical imaging systems that illuminate and display areas of
interest have also been evaluated as navigation aids. These systems
typically have pulsed transmitters and collocated, gated imaging
receivers. The receivers are synchronously gated so that they do
not see backscatter from out-bound transmitter pulses. Current
complementary transmitter/receiver pairs operate at wavelengths
between the visible and the near infrared. Their operation depends
on the reflection contrast between an object and its background.
Such systems inherently have a small field of view, operate at low
transmitter pulse rates, or require long integration periods.
Resulting information rates are too low and the data displayed is
too limited for effective, real time "pilot in the loop"
operation.
A number of systems operating in the microwave, infrared, and
millimeter wave (MMW) regions of the electromagnetic spectrum have
been considered as adverse weather navigation aids. Each takes
advantage of the reduced atmospheric attenuation windows at these
longer than visible wavelengths.
Microwave radiation offers an attractive means to penetrate a low
visibility atmosphere. However, the range-azimuth scan techniques
typically employed to generate a scene and the long operating
wavelengths combine to provide information rates, resolution and
azimuth-elevation display solutions that are inadequate for real
time pilot use as a landing aid.
Infrared systems operating at wavelengths two to twenty times
longer than visible wavelengths offer a resolution comparable to
the human eye as well as provide real-time information presented
directly in azimuth-elevation coordinates. Under haze conditions
and against a terrain background, infrared sensors operating at
wavelengths between 8-12 .mu.m generally provide a better image
than the human eye. However, as weather conditions degrade, their
imaging performance for a visibility less than one-half mile
abruptly deteriorates to levels well below that of the human eye.
Detection capability is also weather limited. Detection is
dependent on the radiant temperature difference between an object
of interest and its background. In many instances, this apparent
difference is less than the sensitivity of practical
state-of-the-art sensors (.about.0.01 C..degree.). This can be
attributed to environmental conditions, such as the twice daily
occurrence of temperature contrast reversal, or the atmospheric
contrast degradation at high humidities that typically accompany
fog conditions. As such, the capabilities of infrared systems are
generally the least effective when they are the most needed.
Infrared systems operating at about 1 .mu.m have been considered to
lessen the effects of these contrast degradation factors by
detecting active rather than passive objects. For example, the
characteristic blackbody radiation from incandescent lamp filaments
is detectable by these infrared systems. This direct radiation
could be detected by the long wavelength radiation emitted by the
heated globe that encloses the filament. However, the magnitude of
the solar background radiation at 1 .mu.m can be as much as 70 db
greater than that of the filament radiation. An intra-scene dynamic
range of about 70 db is therefore required to pull the filament
signal out of the background. This process requires elaborate
signal-background convolutions that are expensive and difficult to
obtain in real time. Moreover, the low solar background advantage
gained by operating in the conventional 3-5 or 8-11 .mu.m windows
is lost.
Prior art systems employing millimeter wave (MMW) radiation have
typically been the best candidates for use in adverse weather. It
is well known that radiation between 30-300 GHz (10-1.0 mm)
penetrates fog and other atmospheric constituents with relatively
modest attenuation. Typically, these systems operate at 35 or 94
GHz where fog penetration is at its greatest. See generally Young
et al., "Passive Millimeter-wave Imaging," TRW Space & Defense
Quest, Winter 1990/91. Millimeter wave systems, however, generally
suffer from some serious disadvantages. Their performance is
degraded in rain, their resolution is inferior to visible sensors,
and their hardware mechanization is complex. Some millimeter wave
systems operate according to conventional radar scanning
principles. The capabilities of these systems are inherently
limited at short final approach ranges when performance is most
demanding for aircraft landings.
MMW systems using alternative imaging techniques are generally
limited in sensitivity and require prolonged dwell times, rendering
them ill-suited to the dynamic environment encountered in the short
final phase of landing. Heterodyning has been considered as a means
to increase sensitivity. However, this gain is realized at the
significant expense in component complexity. Additionally, because
of the long wavelengths involved, millimeter wave systems produce
limiting angular resolutions--six times inferior to that of the
human eye.
Although RF-linked, guidance error based systems provide a desired
immunity to weather, they lack system simplicity as well as
compatibility for "pilot in the loop" operation during landing.
Imaging based systems in turn are simpler and accommodate the
pilot, but lack adequate weather performance. Mixed RF-linked,
earth mapping systems and stored data based systems have also been
developed. They are generally known in the art as synthetic vision
systems, but have not been accepted due their complexity and lack
of a real time, credible image anchored to the runway.
Accordingly, there still exits a need for a system that provides a
compatible combination of characteristics that permits a full range
of operation in adverse weather environments, including real time
"in the loop" operation and resolution comparable to that of the
human eye. Advantageously, such systems would, for example, allow
operators to navigate over local regions in low visibility
conditions in a manner similar to the way those functions are
performed under clear weather conditions.
SUMMARY OF THE INVENTION
A system for providing the location and characteristics of relevant
objects and/or areas, such as aircraft and runway lights, useful
under low visibility conditions is realized by employing
ultraviolet radiation. It has been discovered that the atmospheric
propagation characteristics of low visibility atmospheres permit
the propagation of radiation in the ultraviolet with sufficiently
low attenuation and scattering for use in various applications.
Furthermore, operation in the "solar blind" region of the
ultra-violet radiation, where there is an absence of solar
background radiation, allows a system to image and/or locate
critical markers or areas having associated ultraviolet radiation
sources because of the high signal-to-noise ratio afforded through
the use of high gain imaging tubes.
A system in accordance with the principles of the present invention
comprises one or more ultraviolet radiation sources, a receiver
which is capable of producing an image or representation of the
received radiation, and a display. In one preferred embodiment,
ultraviolet radiation sources are co-positioned with critical
markers, such as runway beacons or hazard annunciators. The
ultraviolet radiation emanates from the source, preferably
modulated to form a repetitive, characteristic signal, propagates
through the low visibility atmosphere, and is received by the
receiver. The receiver may be positioned on a vehicle such as an
aircraft, or fixed at a particular location such as a control
tower. The receiver produces an image or representation of the
received radiation and thereby the critical markers which is then
passed to a display device. The display device is preferably a
transparent head-up display upon which the image or representation
can be superimposed on the real-scene visible image when available
to an operator.
In another preferred embodiment, the source is placed at or near
the receiver, that is, onboard the same vehicle or at the same
fixed location. Retroreflectors are remotely co-positioned with the
critical markers. Modulated ultraviolet radiation is transmitted by
the source and propagates through the low visibility atmosphere to
each retroreflector. The retroreflector reflects the ultraviolet
radiation signal back through the low visibility atmosphere to the
receiver whereupon an image or representation of the received
radiation is presented to an operator by a display device.
In another embodiment, the retroreflectors may be replaced with
transponders. When each transponder receives the ultraviolet
radiation from the source, it transmits differently modulated
ultraviolet radiation back to the receiver. Each transponder may
transmit a unique signal, so that different types of critical
markers can be readily distinguished and displayed to the
operator.
A system in accordance with the principles of the present invention
enables a pilot, vehicle operator, air traffic controller, or other
operator to perform a task in low visibility conditions caused by
fog, rain, or snow, in much the same manner as he would in clear
weather. Specifically, this feature is achieved by combining the
image or representation generated by the present invention with the
real-scene visible view. When an object or target area of interest
marked by a critical marker, such as a beacon, cannot be observed
due to low visibility conditions, an ultraviolet radiation signal
at the same location, generated by a source or from a transponder,
is detected and displayed to the operator at the same location
where the critical marker would be viewed through a clear
atmosphere. This one-to-one mapping can be extended to a field of
sources, reflectors or transponders that form a pattern that
duplicates an existing visible pattern and can then be displayed in
lieu of or in concert with the visible pattern.
BRIEF DESCRIPTION OF THE DRAWINGS
A more complete understanding of the invention may be obtained by
reading the following description in conjunction with the appended
drawings in which like elements are labeled similarly and in
which:
FIG. 1 is a detailed block diagram of a system in accordance with
the principles of the present invention;
FIG. 2 depicts the spectral characteristics of a variety of
ultraviolet sources;
FIG. 3 is a plot of the transmission characteristics of a variety
of absorption filter materials which may be used in the optical
filter of FIG. 1;
FIG. 4 is a plot of the spectral response characteristics of an
ultraviolet microchannel plate photomultiplier tube;
FIG. 5 is a detailed block diagram of another system in accordance
with the principles of the present invention;
FIG. 6 is a plot of the sea-level extinction coefficient as a
function of wavelength for Rayleigh scattering, Mie or aerosol
scattering and ozone absorption in a model clear atmosphere;
FIG. 7 is a graphical illustration of forward scattering of
electromagnetic radiation by an aerosol particle;
FIG. 8 is a representation of the display obtained from
experimental practice for the system of FIG. 1;
FIG. 9 is a response plot showing the angular distribution of the
photon counts per second for the receiver used to obtain the
display of FIG. 8;
FIG. 10 is a pictorial representation of a system in accordance
with the principles of the present invention;
FIGS. 11A-B are pictorial representations of an aircraft attempting
to land in low visibility conditions unaided and aided by the
system of FIG. 1, respectively;
FIGS. 12A-C are illustrations of the pilot's view of the runway
under low visibility conditions from distances of one mile, one
half mile and one quarter mile, respectively;
FIGS. 13A-C are illustrations of the corresponding view of FIGS.
12A-C presented to the pilot through a head-up display in
accordance with the principles of the present invention;
FIGS. 14A-B are illustrations of images driven by a landing
guidance systems on a pilot's head-up display with and without the
use of the present invention;
FIG. 15 is a pictorial representation of the use of a system in
accordance with the principles of the present invention for
monitoring ground traffic by air traffic controllers in low
visibility conditions; and
FIG. 16 is a pictorial representation of the use of a system in
accordance with the present invention to deter runway incursions in
low visibility conditions.
DETAILED DESCRIPTION
A system for providing the location and characteristics of relevant
objects and/or areas in a low visibility atmosphere, useful in
enhancing navigation or surveillance, is realized by employing
ultraviolet radiation in the "solar blind" region. Advantageously,
it has been discovered that radiation in this radiation spectrum
effectively propagates in a low visibility atmosphere for use in
real-time image acquisition applications. Although the prior art
suggests otherwise, it has been discovered that the ozone
absorption in the solar blind region is substantially reduced in a
low visibility atmosphere. Secondly, ultraviolet radiation in a low
visibility atmosphere propagates and/or scatters substantially in a
forward direction. Advantageously, these discoveries coupled with
the absence of solar background radiation in that spectrum allows
the present invention to image and/or locate critical markers or
areas having associated low power ultraviolet radiation sources
because of the high signal-to-noise ratio afforded through the use
of high gain imaging tubes.
The present invention provides distinct advantages over other
currently available technologies. The short wavelength of the
ultraviolet radiation permits the present system to achieve angular
resolutions which are comparable to that of the human eye, a
feature that systems employing long wavelengths, such as millimeter
wave systems, cannot achieve. Receiver information rates are
compatible with the construction of systems that can produce
real-time images corresponding to the real-time scenes. This aspect
permits full "in-the-loop" control. Whereas the performance of most
current systems degrades as visibility conditions worsen, the
performance of the present invention actually improves in more
severe conditions. The necessary components are also much smaller
than the devices of other systems, permitting easy installation
onto aircraft, boats, automobiles, and other vehicles. In addition,
these components are inexpensive, simple, and readily
available.
Without any loss of generality or applicability for the principles
of the present invention, in some embodiments the description is
directed to the aviation industry. It should be understood,
however, that the present invention has many alternative
applications. For instance, the present invention may be used in
maritime navigation, surveillance, or search and rescue
applications.
An exemplary block diagram of a system 100 in accordance with the
principles of the invention is schematically shown in FIG. 1.
Radiation sources 110.sub.1 -110.sub.i, co-positioned or integrated
with critical markers of interest, generate ultraviolet radiation
within the "solar blind" region (.about.0.205-0.275 .mu.m). For
example, sources 110.sub.1 -110.sub.i can be located at or near
visible beacons or lights, such as runway lights. In operation, the
emitted radiation propagates through a low visibility atmosphere
120, such as fog, to a receiver 130. Receiver 130 detects the
incident ultraviolet radiation, while filtering out unwanted
radiation from elsewhere in the spectrum. As low visibility
conditions occur and obscure the location of the critical markers,
an image or representation of the markers can still be acquired and
then displayed because the ultraviolet radiation penetrates through
low visibility atmosphere 120.
Each source 110.sub.1 -110.sub.i includes an ultraviolet lamp 150,
beam forming optics 160 and a modulator 170. Lamp 150 may be
constructed from a variety of light sources, such as xenon and
mercury flashlamps which emit radiation in the desired ultraviolet
spectrum. Alternatively, UV lasers, such as a frequency doubled
Nd:YAG laser may be used. In the latter case, electro-optical or
mechanical scanners may be used to direct the laser radiation along
a desired solid angle.
FIG. 2 includes typical plots of the spectral characteristics of
several light sources that may be used for lamp 150. Preferably,
lamp 150 emits radiation between 0.205 .mu.m-0.275 .mu.m over a
broadband wavelength spectrum or at discrete wavelengths.
Preferably, modulator 170 modulates the radiation generated by lamp
150 to form a repetitive, characteristic radiation pattern which
can be use to distinguish it from other possible sources of
ultraviolet radiation. Optics 160 is used to direct the ultraviolet
radiation within a desired solid angle of illumination.
Receiver 130 comprises a lens 180, an optical filter 190, an
imaging tube 200 and a signal processor 210. The field of view
(FOV) of lens 180 is preferably 30.degree. horizontally and
22.5.degree. vertically, but these values can vary from a few
degrees to 120.degree.. Lens 180 made of UV quartz or other UV
transmissive material is typically 1"-4" in diameter which compares
favorably with the 12"-24" diameter lenses required by millimeter
wave systems. The angular resolution of receiver 130 is generally
comparable to that of the human eye, typically about 1-2 mrads.
Optical filter 190 is a bandpass filter that passes radiation at
wavelengths approximately between 0.205 .mu.m-0.275 .mu.m.
Substantial roll-off is used to attenuate solar radiation at
wavelengths above 0.275 .mu.m. Preferably, filter 190 attenuates
about an order of magnitude per nanometer between .about.0.275
.mu.m-0.290 .mu.m. It is contemplated that filter 190 may comprise
absorption bandpass filters and/or comprise reflective filters in
cascade. Various materials can be used. For example, filter 190 may
be partially constituted from NiSO.sub.4 (H.sub.2 O).sub.6 and
Cation X which have response characteristics as shown in FIG. 3.
See The Middle Ultraviolet by A. E. S. Green, John Wiley &
Sons, New York (1966). Alternatively, narrow bandpass filters or
interference filters may be used, which are well known in the art,
such as for use with narrow line emission sources, such as lasers.
Also, dichroic mirrors and multilayer coated mirrors may be used to
reflect only the radiation spectrum of interest to imaging tube
200.
Preferably, imaging tube 200 is a "solar blind" microchannel plate
photomultiplier tube (MCP), such as the MCPT manufactured by EMR
Photoelectric of Princeton, N.J., which operates at or near the
theoretical limit of sensitivity. Other suitable high gain imaging
detectors may be used, such as solid state CCDs, image intensifiers
and the like. Although solid state CCDs do not posses the same
sensitivity, they may be suitable at shorter ranges where the
radiation intensity is substantially at a higher level. CCDs, for
example, may also be used in conjunction with the MCPs to achieve
system redundancy necessary for aviation. In the event of
malfunction, CCDs can be used at short ranges in the final critical
moments of landing, thereby providing graceful system degradation
rather than catastrophic failure.
Those skilled in the art will readily note that an MCP is an image
tube which detects a radiant image by counting individual photons
and registering their spatial relationship. Because the system
operates in the "solar blind" region where there is substantially
no solar background radiation, this method of detection affords a
high signal-to-noise ratio. Specifically, a MCP operates in the
following manner. Radiant energy is focused on a photocathode which
emits primary electrons to a parallel array of glass cylinders
about 10 .mu.m in diameter and 1 mm in length. The inside walls of
the cylinders are coated with a secondary emitting material. The
primary electrons strike the inside Walls near the entrance end and
cause secondary electrons to be emitted. These secondary electrons
in turn strike the wall further into the depth of the cylinder and
create additional secondary electrons. This cascading mechanism
produces a high, noise-free gain, typically on the order of
10.sup.6. For a more complete description of ultraviolet
microchannel plates see C. B. Johnson et al., "Ultraviolet Sensing
Technology Developments at ITT", SPIE Ultraviolet Technology,
150-54 (1986); and the RCA Electro-Optics Handbook, RCA Solid State
Division, Lancaster, Pa. (1974).
Shown in FIG. 4 is a typical spectral response of imaging tube 200.
Since there is a significant spectral response at wavelengths above
0.275 .mu.m, the cutoff characteristics of optical filter 190
should be tailored to reject radiation above 0.275 .mu.m so as to
limit detection to the solar blind region. Imaging tube 200
generates an image or representation of sources 110.sub.1
-110.sub.i at a resolution of .about.512.times.512 pixels.
Those skilled in the art will appreciate the fact that due to the
absence of solar background radiation at night the inherent
spectral response of imaging tube 200 may obviate the need for
filter 190. Accordingly, filter 190 may be automatically removed
from the optical path of incident radiation through a mechanical or
optical mechanism when solar background radiation is not detected.
This can be effected through the use of a detector responsive to
the characteristics of the solar background radiation.
Signal processor 210 processes the image from imaging tube 200 so
as to filter out those undesired signals corresponding to radiation
that is unmodulated, such as those generated from street lamps,
fires, lightning flashes and the like. Signal processor 210 can
also discern among signals corresponding to radiation modulated at
different frequencies. Such modulation, either FM, PCM or AM, can
be imposed on the ultraviolet sources associated with critical
markers of interest so as to provide each with an identifying
characteristic. Those identifying characteristics, for example, may
be used to distinguish between hazard annunciators atop buildings,
obstructions, and/or the color or type of the runway lights.
Information processed by signal processor 210 is fed to display 140
so that an image or representation of the desired critical markers
can be displayed to an operator. Those skilled in the art will
recognize that the image or representation of the sources produced
from receiver 130 may be subject to a wide variety of image
processing techniques. See Digital Image Processing by Pratt, John
Wiley & Sons, New York (1978). Display device 140 is preferably
a transparent head-up display, helmet-mounted sight, visor, or a
device that displays the image or representation on a medium
interposed between the operator's eye and his view of the actual,
related scene. Alternatively, the image can be displayed on a
monitor or integrated with the display of another sensor, such as a
radar display.
Those skilled in the art will recognize that signal processor 210
may include a micro-processor based device, A/D converters, control
logic, software, and other associated electronics. The construction
of such devices is well known in the art and hence will not be
discussed here.
An alternative block diagram of a system in accordance with the
principles of the invention is schematically shown in FIG. 5. This
alternative embodiment is similar to that of FIG. 1, except that
reflectors 151.sub.1 -151.sub.i are co-positioned or integrated
with the critical markers of interest. Likewise, radiation source
110.sub.1 generates ultraviolet radiation in the "solar blind"
region. However, source 110.sub.1 is substantially co-located with
receiver 130, rather than being separated by low visibility
atmosphere 120.
In operation, radiation from source 110.sub.1 propagates through
low visibility atmosphere 120 to reflectors 151.sub.1 -151.sub.i.
Each of reflectors 151.sub.1 -151.sub.i reflects or redirects the
radiation back through low visibility atmosphere 120. Receiver 130
detects that radiation and similarly produces an image or
representation of the radiation from reflectors 151.sub.1
-151.sub.i, which is then displayed on display 140.
Because source 110.sub.1 and receiver 130 are located in close
proximity to each other, such as on an aircraft, it is necessary to
prevent receiver 130 from detecting backscatter from source
110.sub.1. Signal processor 210 can perform this task by gating
source 110.sub.1 and receiver 130. When source 110.sub.1 is
transmitting, signal processor 210 signals imaging tube 200 to
cease or inhibit detection. This is accomplished through gate
signal 520. When transmitting has ceased, gate signal 520 is
removed shortly thereafter and imaging tube 200 detects the
radiation from reflectors 151.sub.1 -151.sub.i. To facilitate
gating, signal processor 210 can also signal modulator 170 through
signal 510 to start transmission.
It is contemplated that reflectors 151.sub.1 -151.sub.i may be
retroreflectors. A retroreflector is a device which reflects
radiation substantially back along the path of the incident
radiation. Because receiver 130 and source 110.sub.1 are located in
close proximity, any reflected radiation will be substantially
detected by receiver 130. Retroreflectors may take many forms, such
as corner cube prisms, spheres and the like.
It is also contemplated that incident radiation returning to
receiver 130 can be modulated so as to enhance detection or impose
other desired information thereon. This modulation, for example,
can be effected through the use of mechanical, electrical or
optical shutters which are well known in the art.
Alternatively, reflectors 151.sub.1 -151.sub.i can be replaced with
transponders that retransmit the incident radiation at a greater
intensity level. Each transponder itself includes, for example,
receiver 130 and source 110 and may be designed to modulate the
radiation in accordance with additional information. For example,
the ultraviolet radiation signal from source 110.sub.1 can be used
to trigger each transponder to transmit a unique return radiation
signal representing a different type of hazard or runway light.
These different radiation signals can be distinguished by colors,
shading, or other information on display device 140.
To more fully appreciate the principles of the present invention,
it will be instructive to discuss briefly the propagation of
electromagnetic radiation. Radiation from a source propagating
through a gaseous atmosphere has an irradiance E given by: ##EQU1##
where I is the intensity of source radiation, R is the distance
from the source, and T.sub.a is the atmospheric transmittance.
T.sub.a ranges from unity which represents perfect transmittance to
zero representing total extinction. This transmittance T.sub.a
represents the decrease in radiant intensity due to absorption and
scattering and is a function of many variables, including
wavelength, path length, pressure, temperature, humidity, and
atmospheric composition.
More specifically, the atmospheric transmittance T.sub.a is given
by Beer's Law:
where .alpha. is the spectral attenuation coefficient or
"extinction coefficient." The extinction coefficient .alpha. is
wavelength dependent and is a measure of the extent of absorption
and scattering of the radiation by the atmosphere. See, RCA
Electro-Optics Handbook, RCA Solid State Division, Lancaster, Pa.
(1974).
Attenuation is the result of scattering and absorption. Scattering
effects are produced by two principal mechanisms, scattering by air
molecules, called "Rayleigh" scattering, and scattering by larger
aerosol particles, referred to as "Mie" scattering. See Principles
of Optics by Born and Wolf, Pergamon Press, New York (1975).
Although a wide variety of constituents are responsible for
absorption, the effects of ozone O.sub.3 and oxygen O.sub.2 are the
most pronounced in the ultraviolet region of interest. Ozone
absorption dominates in clear weather.
The extinction coefficients for each source of attenuation can be
determined separately. Shown in FIG. 6 is the sea-level extinction
coefficient as a function of wavelength for Rayleigh scattering
(.alpha..sub.RAYLEIGH), aerosol scattering (.alpha..sub.AEROSOL),
and ozone absorption (.alpha..sub.OZONE). The individual extinction
coefficients sum to show the total extinction coefficient (.alpha.)
for the atmosphere. The amount of absorption and scattering
occurring in the atmosphere, as measured by the extinction
coefficient .alpha., has a profound effect on the visibility
through the atmosphere.
From the extinction coefficient plots of FIG. 6, the prior art
suggests that ultraviolet radiation will be more severely
attenuated than visible radiation. Although ozone produces
negligible attenuation in most areas of the electromagnetic
spectrum, it is responsible for a dramatic absorption effect in the
ultraviolet region. Below about 0.21 .mu.m, oxygen significantly
begins to contribute to the absorption.
A combination of various phenomena has been discovered that permits
ultraviolet radiation to penetrate low visibility environments.
First, it has been discovered that the ozone absorption effect is
significantly reduced in fog which results when water molecules in
the atmosphere condense to form small water droplets (10-20 .mu.m
in diameter) that remain suspended in the air. Water droplets that
contribute to the adverse weather condition interact with the ozone
molecules and break them down to molecular and atomic oxygen.
Advantageously, this results in a reduction in that portion of the
extinction coefficient attributable to ozone, .alpha..sub.OZONE.
Ozone in the local atmosphere will be further depleted as the
adverse weather condition, and therefore the visibility, worsens.
In other words, the ozone absorption in the ultraviolet region
reduces as visibility conditions become more severe. Further, the
fact that ozone naturally decomposes at night, reaching a minimum
in the morning when low visibility conditions are most prevalent
can be used to an advantage.
Although ultraviolet radiation is significantly scattered by the
water droplets present in the low visibility environment, it has
also been discovered that a significant portion propagates and/or
scatters in a substantially forward direction, as illustrated in
FIG. 7, and hence is not attenuated. Also, a sufficient amount of
energy propagates on-axis such that the location of its source can
be determined with good resolution. There is still, however,
significant attenuation in the ultraviolet region in adverse
weather conditions. But the absence of any solar background
radiation in that spectrum allows high-gain image tubes, such as
microchannel plate tubes, to be used to localize and image the
source of the radiation from the extremely low radiation
detected.
Experimental results obtained at the airport in Williamsport, Pa.
demonstrate the use of ultraviolet radiation in the solar blind
region to penetrate a low visibility atmosphere. The Williamsport
airport was selected for its prevailing susceptibility to dense fog
situations. Under measured visibility conditions of 700 feet
(measured by an FAA approved visual range meter), two tungsten
halogen sources spaced six feet apart were located 2400 feet from
receiver 130. These two sources were clearly and separately
detected and displayed as shown in FIG. 8. The images 810 and 820
of the respective sources are not horizontal because of a
misalignment of the imaging tube during the experiment. FIG. 9
provides the same results in a different format. These figures
confirm that ultraviolet signal radiation propagates and/or
scatters in a substantially forward direction through a low
visibility atmosphere. Furthermore, the distinct separation of the
two sources confirms the ability of the present invention to image
with an angular resolution (.about.2.5 milliradians) comparable to
that of the human eye, at least under those conditions.
To appreciate the advantages of the present invention, the aviation
industry's current methods of dealing with visibility problems are
examined. Low visibility conditions are categorized for aviation
purposes by the FAA as shown in the table below.
______________________________________ Weather Minima For Aircraft
Landings Decision Height Runway Visual Range Category (ft.) (ft.)
______________________________________ I 200 2400 II 100 1200 IIIa
0 700 IIIb 0 150 IIIc 0 0
______________________________________
Each landing category has an associated runway visual range based
on the distance at which an object with a 5% contrast can be
detected. The precision landing equipment employed by the aircraft
and the airport is certified according to their collective ability
to provide guidance for safe landing under the various low
visibility conditions indicated in the table. If the runway visual
range becomes less than that associated with a given category of
the precision landing system, that particular grade system cannot
be used for the approach and landing. For example, if the pilot of
an aircraft equipped with a CAT II precision landing system is on a
final approach to landing and he cannot see the runway at an
altitude of 100 ft, corresponding to a visual, and at a range of
1,200 ft, the pilot must execute a missed approach.
The precision landing equipment necessary to land in each category
becomes progressively more complex and costly as the low visibility
condition becomes more severe. Because of such expense, a very
small fraction of airports and aircraft have CAT IIIa landing
capability, and less than ten facilities have fully certified CAT
IIIc capability. One of the advantage of the present invention lies
in permitting landing in more severe adverse weather than an
aircraft or airport's precision landing system capability would
normally allow. For instance, commercial airlines have expressed
the desire that a CAT I equipped aircraft be able to land in CAT
IIIa visibility conditions. This would require the ability to see
the runway at an altitude of 200 ft and a range of 2400 ft under
700 ft visibility conditions. Such a capability would provide
significant economic and operational benefits since it would open
up for service hundreds of airports that are now closed during
adverse weather.
Turning to FIG. 10, there is shown a pictorial representation of a
system in accordance with the block diagrams of FIGS. 1 and 5 for
facilitating aircraft landing under adverse weather conditions.
Ultraviolet radiation, within the solar blind spectrum of 0.205
.mu.m-0.275 .mu.m, is emitted from radiation sources 110.sub.1
-110.sub.i. Sources 110.sub.1 -110.sub.i are situated at, near or
integrated with the runway edge and centerline lights. Preferably,
sources 110.sub.1 -110.sub.i are installed within the runway edge
and centerline lights, such as edge runway lights Model HRLQ
manufactured by Crouse-Hinds Airport Lighting Products, of Windsor,
Conn. and centerline lights Model RCL-20560P2 manufactured by Sepco
Aviation Lighting, Inc., of Windsor, Conn. Preferably, sources
110.sub.1 -110.sub.i emit radiation at varying azimuth angles at a
peak elevation angle of 3.degree..
Alternatively, the centerline and edge runway lights may be
modified with lamps that advantageously emit a portion of their
radiation in the desired ultraviolet region. In this manner, the
runway lights function as both the visible markers and the
ultraviolet sources. In some instances, the lamps may not have to
be modified. Quartz tungsten halogen lamps, already in use in many
runway installations, emit sufficient radiation in the ultraviolet
region if operated at blackbody temperatures in the region of 3000
K.degree.. See "Tungsten Halogen for Illumination" in The Photonics
Design and Applications Handbook (1993). In some instances, the
lamp's globe or lens, which modifies the radiation pattern, may
have to be replaced with those transmissive in the ultraviolet
region of interest.
The emitted ultraviolet radiation propagates through low visibility
atmosphere 120 and is received by receiver 130 that is located
onboard an aircraft 1035. As discussed above, receiver 130 includes
solar blind imaging tube 200 (shown in FIGS. 1 and 5) capable of
producing an image or spatial representation of the received
radiation. Display device 140 presents to the pilot an image or
representation of sources 110.sub.1 -110.sub.i. Receiver 130 may
detect scattering in the form of a halo from sources that are
several hundred feet away. The forward scattering property of the
radiation of interest will cause the halo to be substantially
concentrated about its source of origin and hence amenable to
signal processing. Any of a wide variety of anti-blooming
techniques well known in the art may be used to eliminate the
presence of such halo effects in the image that is ultimately
displayed. Such techniques allow both near and far field images to
be displayed with virtually no loss in angular resolution. Image
processing techniques may also be employed to accomplish automated
locating and tracking for use in "out of the loop" landings.
Alternatively, the ultraviolet radiation can be emitted from an
appropriate source located onboard aircraft 1035. Likewise, the
ultraviolet radiation propagates through low visibility atmosphere
120 until it encounters reflectors 151.sub.1 -151.sub.i located at,
near or integrated with the runway edge and centerline lights.
Reflectors 151.sub.1 -151.sub.i reflect the incident ultraviolet
radiation back through low visibility atmosphere 120. That
radiation is then detected by receiver 130 which similarly produces
an image or spatial representation of reflectors 151.sub.1
-151.sub.i. Again display device 140 presents an image or
representation of the reflectors to the pilot. In this manner, a
pilot is able to "see" the runway, even in low visibility
conditions, thereby allowing him to safety land the aircraft.
Shown in FIG. 11A is a pictorial representation of an aircraft
attempting to land under one quarter mile visibility without the
use of the present invention. The plane at the ranges of one mile,
one half mile and one quarter mile from the runway are indicated by
the numerals 1, 2 and 3, respectively. The light cone indicates the
distance at which the pilot can see through the fog. The
corresponding visible images available to the pilot at those
respective positions are shown in FIGS. 12A-C. In this example, the
pilot suddenly encounters fog at a distance of one quarter mile and
his vision of the runway is obscured, as depicted in FIG. 12C.
For comparison, shown in FIG. 11B is a pictorial representation of
the same aircraft landing with the use of the present invention.
Similarly, the numerals 1, 2 and 3 depict the plane at the same
distances away from the runway as in FIG. 11A. Further, shown in
FIGS. 13A-C are pictorial representations of the display seen by
the pilot on display 140 at a range of one mile, one half mile, and
one quarter mile, respectively. It should be noted that the pilot
continues to enjoy a one mile visibility despite the sudden outset
of fog.
It will be apparent to those skilled in the art that the present
invention may be used with current landing guidance commands
generated by existing landing systems, such as GPS/GNSS, ILS or
MLS. FIG. 14A shows a representation of the orientation of a flight
vector generated on a head-up display that is oriented by such
guidance commands. A pilot controls his aircraft such that he
maintains the orientation of this vector either centered amidst the
two sets of indices or circumscribed about a guidance ball. Shown
in FIG. 14B is the same flight vector superimposed with an image of
the actual location of the runway lights as detected by the present
invention. The simultaneous display of navigation information from
two distinctly different sources, provides a vital cross check
during the most critical phase of flight. This cross check
"unloads" a flight crew of concerns and frees them to perform other
tasks, thereby enhancing safety.
In another embodiment, the receiver and display can be installed in
airport control towers to assist in ground surveillance during low
visibility conditions. In addition to the runway beacons,
ultraviolet sources can be placed on all aircraft and co-positioned
or integrated with existing visible beacons (shown as beacon 145 in
FIG. 10). An image of the airport runways with taxiing aircraft
traffic can be presented in a head-up display to the air traffic
controllers or projected onto the control tower windows. A
pictorial representation of this implementation is shown in FIG.
15. Taxiing aircraft 1530 and ground vehicles 1510 are retrofitted
with sources 110.sub.1 -110.sub.i. Ultraviolet radiation propagates
to control tower 1520 where receiver 130 and display 140 are
installed. An illustration of air traffic controllers using the
images presented by the present invention to control the ground
traffic is shown in the cut away view of tower 1520.
Each source can be modulated or encoded to uniquely identify each
aircraft. Moreover, a video tracking box can continuously and
automatically adjust its size to ensure that it completely encloses
the aircraft target, yet excludes other targets from entering the
box. This auto-track procedure, with a separate gate for each
aircraft, provides for a performance superior to radar systems. As
such, there is a low probability of cross-target capture that can
occur with "track while scan" systems. Moreover, the modulated or
encoded radiation may be used for "de-cluttering." Various objects
and/or areas may be removed from the display by filtering out the
modulated signals that are associated with those objects and/or
areas.
Many control towers currently use large monitors that display a
layout of the airport runways and taxiways. The location of the
aircraft and ground vehicles can be superimposed onto those
monitors at their appropriate location, much like weather satellite
images are superimposed over a representation of the land mass.
Since this display format is familiar to air traffic controllers,
it facilitates the use of the present invention.
Taxiing aircraft can also use the present invention as they move to
and from the runway. Ultraviolet sources co-positioned with the
existing visible beacons define the taxiing paths, and ultraviolet
sources co-positioned with existing aircraft beacons can inform the
pilot of the presence of other aircraft. Preferably, these
ultraviolet sources are pulsed xenon sources. As shown pictorially
in FIG. 16, the use of the present invention by landing aircraft,
taxiing aircraft, and by the control tower provides multiple
deterrents to runway incursions in low visibility conditions.
Receiver 130, display 140 and an aircraft beacon with an
ultraviolet source are installed on taxiing aircraft 1530. This
same equipment is also installed on landing aircraft 1035. Control
tower 1520 likewise possesses a receiver and display. In this
manner, the personnel in landing aircraft 1035, taxiing aircraft
1530 and in tower 1520 can see the moving traffic in the air and on
the runways. The pilot's view in taxiing aircraft 1530 is depicted
in the upper right. The runways and landing aircraft 1035 can be
clearly seen. The air traffic controller, whose view is depicted in
the top center can monitor both taxiing aircraft 1530 and landing
aircraft 1035. The pilot of landing aircraft 1035 can clearly see
the runway and the taxiing aircraft in his view, as depicted in the
lower left. In this fashion, the present invention provides the
potential for a three-pronged deterrent to runway incursions.
It should be understood that although the present invention is of
incalculable benefit to the aviation industry, applications of the
present invention are in no way limited to its use in aircraft. For
instance, the system can be used to effect search and rescue. A
stranded watercraft could employ an ultraviolet source or reflector
to assist a search plane or boat equipped with the present
invention to locate the watercraft in adverse weather.
Also, the present invention may be used to realize obstruction
detection and collision avoidance. Ultraviolet sources may be
co-positioned with hazard beacons which inform aircraft of the
presence of buildings, radio antennae, power lines, etc. The
present invention may also be used to permit navigation in
dangerous terrain areas which currently present perilous situations
during low visibility conditions. For example, take-offs and
landings at airports in mountainous regions are presently curtailed
in fog conditions because of the significant risk of aircraft
collision with the terrain. However, sources, reflectors or
transponders could be affixed to mountain slopes, peaks and other
terrain obstacles enabling the present invention to provide their
location to pilots. Such information may also be used to indicate
the proper flight path in and out of the region.
A system in accordance with the present invention can also be of
significant use to the maritime community. For example, it is the
current practice to define preferred waterway traffic channels by
using navigation buoys. A watercraft navigates in the channel by
traveling within boundaries defined by buoys. These buoys are often
difficult to locate amid heavy ship and boat traffic, wave swells,
ground clutter and precipitation. The present invention can
alleviate this navigation difficulty. Ultraviolet sources or
reflectors may be placed on the buoys and a receiver installed in
the watercraft. The location of the buoys can be displayed on a
head-up display in the cabin of the ship, or superimposed on the
cabin window. In this manner, the ship captain can identify the
navigation buoy and steer his craft accordingly.
Even more advantageously, the location of the buoys may be used to
annotate an existing radar display. Normally, the radar system
provides the location of objects, but leaves the identification of
those objects to the radar operator. Data from the present
invention can be used to automatically identify the navigation
buoys and present that information on the radar display, thus
providing a diagram of the proper water channel to travel.
Because of the unique identification capability inherent in using
modulated ultraviolet radiation, a large number of objects may be
separately located and identified and annotated on the radar
display, including hazard annunciators on obstacles, RACON beacons
on bridges and running lights on other watercraft. Sources,
preferably UV lasers, may also be co-positioned with range light
elements.
Also, the present invention may be installed in automobiles. For
instance, ultraviolet sources or reflectors can be placed alongside
the roadside edge. A receiver and display device inside an
automobile can assist a driver in maintaining his position on the
roadway during dense fog conditions. Indeed, the present invention
can play a role in virtually any application where it is necessary
to be able to see through a low visibility environment and quickly
react.
It should be understood that various other modifications will also
be readily apparent to those skilled in the art without departing
from the scope and spirit of the invention. Accordingly, it is not
intended that the scope of the claims appended hereto be limited to
the description set forth herein, but rather that the claims be
construed as encompassing all the features of the patentable
novelty that reside in the present invention, including all
features that would be treated as equivalents thereof by those
skilled in the art to which this invention pertains.
* * * * *